Molding machines such as those which are used to mold concrete blocks and similar products are typically large, heavy and noisy. In the commercial production of concrete blocks, higher speed operation of the molding machines and a more uniform quality of the blocks produced is accomplished by vibrating the mold during the block formation. This reduces the time necessary to compact the concrete into the mold and minimizes the possibility of the formation of voids in the blocks produced.
Blocks produced in a concrete block molding machine are stripped from the molds and placed on pallets used to convey the green or uncured blocks from the mold. The pallet generally is located beneath the open bottom of the mold and serves to close the bottom of the mold during the molding operation. In the past, when the mold was vibrated, with or without simultaneous vibration of the pallet, the mold assembly and pallet tended to separate during each cycle of vibration, causing substantial noise and allowing some leakage of the block material between the mold and pallet, resulting in the formation of burrs on the bottom of the blocks.
In order to overcome the problems of separation of the mold and pallet and thereby eliminate burrs from the bottoms of the blocks, some attempts have been made in the past to clamp together the mold and pallet during the vibration cycle of operation of the mold making machine; so that the mold and pallet vibrate together as a unit. One such prior art solution is disclosed in the U.S. Pat. No. 2,342,440 to Whitsitt, issued Feb. 22, 1944. In the Whitsitt patent a clamping mechanism in the form of pivoted hooks is used to secure the mold box, pallet and pallet support table together during the vibration cycle of operation. No isolation of these vibrating parts from the main frame of the machine is present, however; so that substantial stress is placed on the machine frame during its operation. In fact, without vibration isolation, extensive heavy and expensive anchoring techniques must be employed to prevent the machine from bouncing around and moving from its position during its operation. The vibration which is imparted to the main frame of the machine rapidly accelerates fatigue which can lead to premature failure of the machine. Such failure necessitates expensive repairs and lost time during periods of inoperation for purposes of repairing the machine. In addition, the pivotal clamps used in the machine of the Whitsitt patent are subjected to considerable strain at the pivot point and require relatively complex operating mechanisms to move them between their open and closed or clamped positions.
Another attempted solution in the prior art is disclosed in U.S. Pat. No. 3,660,004, to Robert J. Woelk, issued May 2, 1972. This patent also discloses concrete block molding machinery having apparatus for moving a block receiving pallet against the mold assembly used in forming the concrete blocks. An auxiliary table carried by the main pallet support table has rotatable clamp arms on it for engaging clamp receiving members on the mold box, and these arms are movable in and out of engagement with the receiving members on the mold box to correspondingly clamp the auxiliary table, pallet and mold box together during the vibration portion of the cycle of operation of the machine. The arms are subsequently disengaged to permit stripping of the mold and removal of the pallet during other portions of the machine operation.
As with Whitsitt, the apparatus disclosed in the Woelk patent does clamp the pallet tightly against the bottom of the mold box during the vibration operation; so that the elimination of burrs from the bottom of the blocks is effected. Woelk, however, requires an auxiliary pallet support table in addition to the main pallet support table; and the entire assembly of mold box, pallet and auxiliary pallet support table rests on top of the main pallet support table during the vibration operation. Resilient upper surfaces are provided on the main pallet support table in an attempt to isolate vibration of the mold box/pallet assembly from the rest of the machine, but necessarily these surfaces must be fairly rigid to permit their main function of serving as a firm support for the pallet in the machine. As a consequence, substantial vibration is imparted to the main pallet support table and from it to the main machine frame when the machine of Woelk is operated. As a consequence, the problems inherent with transmitting the vibration of the mold box to the main machine frame, discussed above in conjunction with the Whitsitt patent, are inherent also in apparatus built in accordance with the Woelk patent.
The machine of the Woelk patent also uses rotatable clamping arms to effect the clamping operation, and the mechanism for moving these arms from the unclamped to the clamped position and back again is quite complicated. This results in higher initial manufacturing costs; and in the hostile environment in which the machine is operated, inherently results in increased maintenance costs because of the number of different parts which are likely to fail in the operation of such a machine.
In addition to the disadvantages noted above in prior art molding machines, such as concrete block making machines, the noise produced by such machines is deafening and far exceeds acceptable work environment standards. As a consequence, it is desirable to provide a simplified concrete block making machine which has the advantages of clamping the pallet firmly against the bottom of the mold during the vibration portion of the machine operation to eliminate noise caused by the mold hitting the pallet and which also uses a simplified mechanism for achieving this result. Also, it is desirable to reduce the noise of operation of concrete block making machines and further to isolate the vibration only to those parts of the machine which must be vibrated to accomplish the desired results of improved molding of concrete blocks and similar products.